Brainfuck Hello World实际如何运作? [英] How does the Brainfuck Hello World actually work?
问题描述
有人将此邮件发送给我，并声称这是Brainfuck的世界(我希望如此...)
Someone sent this to me and claimed it is a hello world in Brainfuck (and I hope so...)
++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>.
我知道它可以通过移动指针，递增和递减的东西来工作的基础知识...
I know the basics that it works by moving a pointer and increment and decrementing stuff...
但是我仍然想知道，它实际上是如何工作的?首先如何在屏幕上打印任何内容?它如何编码文本?我根本听不懂...
Yet I still want to know, how does it actually work? How does it print anything on the screen in the first place? How does it encode the text? I do not understand at all...
推荐答案
1.基础
要了解Brainfuck，您必须想象无限个由0初始化的单元格的数组.
1. Basics
To understand Brainfuck you must imagine infinite array of cells initialized by 0 each.
...[0][0][0][0][0]...
当Brainfuck程序启动时，它指向任何单元格.
When brainfuck program starts, it points to any cell.
...[0][0][*0*][0][0]...
如果将指针右移>，则将指针从单元格X移动到单元格X + 1
If you move pointer right > you are moving pointer from cell X to cell X+1
...[0][0][0][*0*][0]...
如果增加单元格值+，则会得到:
If you increase cell value + you get:
...[0][0][0][*1*][0]...
如果再次增加单元格值+，则会得到:
If you increase cell value again + you get:
...[0][0][0][*2*][0]...
如果减小单元格值-，则会得到:
If you decrease cell value - you get:
...[0][0][0][*1*][0]...
如果将指针向左移动<，则将指针从单元格X移动到单元格X-1
If you move pointer left < you are moving pointer from cell X to cell X-1
...[0][0][*0*][1][0]...
2.输入
要读取字符，请使用逗号,.它的作用是:从标准输入中读取字符，并将其十进制ASCII码写入实际单元格.
2. Input
To read character you use comma ,. What it does is: Read character from standard input and write its decimal ASCII code to the actual cell.
看看 ASCII表.例如，!的十进制代码是33，而a的十进制代码是97.
Take a look at ASCII table. For example, decimal code of ! is 33, while a is 97.
好吧，让我们想象一下您的BF程序内存如下:
Well, lets imagine your BF program memory looks like:
...[0][0][*0*][0][0]...
假设标准输入代表a，如果使用逗号,运算符，则BF会执行以下操作:a十进制ASCII码97读入内存:
Assuming standard input stands for a, if you use comma , operator, what BF does is read a decimal ASCII code 97 to memory:
...[0][0][*97*][0][0]...
您通常想以这种方式思考，但是事实要复杂一些.事实是BF不会读取字符，而是读取一个字节(无论该字节是什么).让我给你举个例子:
You generally want to think that way, however the truth is a bit more complex. The truth is BF does not read a character but a byte (whatever that byte is). Let me show you example:
在Linux中
$ printf ł
打印:
ł
是特定的波兰字符.此字符未通过ASCII编码进行编码.在这种情况下，它是UTF-8编码，因此它过去在计算机内存中占用一个以上的字节.我们可以通过进行十六进制转储来证明这一点:
which is specific polish character. This character is not encoded by ASCII encoding. In this case it's UTF-8 encoding, so it used to take more than one byte in computer memory. We can prove it by making a hexadecimal dump:
$ printf ł | hd
其中显示:
00000000 c5 82 |..|
零偏移. 82是第一个字节，c5是第二个字节，代表ł(我们将按顺序读取它们). |..|是图形表示，在这种情况下是不可能的.
Zeroes are offset. 82 is first and c5 is second byte representing ł (in order we will read them). |..| is graphical representation which is not possible in this case.
好吧，如果将ł作为输入传递给读取单字节的BF程序，则程序存储器将如下所示:
Well, if you pass ł as input to your BF program that reads single byte, program memory will look like:
...[0][0][*197*][0][0]...
为什么197? 197十进制是c5十六进制.看起来很熟悉?当然.它是ł的第一个字节！
Why 197 ? Well 197 decimal is c5 hexadecimal. Seems familiar ? Of course. It's first byte of ł !
要使用点.打印字符，它的作用是:假设我们将实际单元格值视为十进制ASCII码，则将相应字符打印到标准输出.
To print character you use dot . What it does is: Assuming we treat actual cell value like decimal ASCII code, print corresponding character to standard output.
好吧，让我们想象一下您的BF程序内存如下:
Well, lets imagine your BF program memory looks like:
...[0][0][*97*][0][0]...
如果现在使用点(.)运算符，则BF会执行以下打印:
If you use dot (.) operator now, what BF does is print:
a
因为ASCII中的a十进制代码为97.
Because a decimal code in ASCII is 97.
例如，这样的BF程序(97加2点):
So for example BF program like this (97 pluses 2 dots):
++++++++++++++++++++++++++++++++++++++++++++++++ ++++++++++++++++++++++++++++++++++++++++++++++++++++++ ..
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++..
将其指向的单元格的值增加到最多97，然后将其打印2次.
Will increase value of the cell it points to up to 97 and print it out 2 times.
aa
4.循环
在BF循环中，循环由循环开始[和循环结束]组成.您可以认为这就像在C/C ++中，条件是实际单元格值.
4. Loops
In BF loop consists of loop begin [ and loop end ]. You can think it's like while in C/C++ where the condition is actual cell value.
在下面看看BF程序:
++[]
++将实际单元格值增加两次:
++ increments actual cell value twice:
...[0][0][*2*][0][0]...
[]就像while(2) {}，所以它是无限循环.
And [] is like while(2) {}, so it's infinite loop.
让我们说我们不希望这个循环是无限的.我们可以例如:
Let's say we don't want this loop to be infinite. We can do for example:
++[-]
因此，每次循环循环都会减少实际单元格值.一旦实际单元格值为0，循环结束:
So each time a loop loops it decrements actual cell value. Once actual cell value is 0 loop ends:
...[0][0][*2*][0][0]... loop starts
...[0][0][*1*][0][0]... after first iteration
...[0][0][*0*][0][0]... after second iteration (loop ends)
让我们考虑另一个有限循环的例子:
Let's consider yet another example of finite loop:
++[>]
此示例显示，我们尚未在循环开始于的单元格处完成循环:
This example shows, we haven't to finish loop at cell that loop started on:
...[0][0][*2*][0][0]... loop starts
...[0][0][2][*0*][0]... after first iteration (loop ends)
不过，好的做法是在我们开始的地方结束.为什么 ?因为如果循环结束了它开始的另一个单元格，则我们无法假定单元格指针将位于何处.老实说，这种做法可以减少脑筋.
However it is good practice to end where we started. Why ? Because if loop ends another cell it started, we can't assume where the cell pointer will be. To be honest, this practice makes brainfuck less brainfuck.
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